This invention relates generally to the manufacture and use of an infusion cannula suitable for subcutaneous implantation. The infusion cannula is capable of controlled release of an gent that facilitates maintenance of the infusion site.
Subcutaneous infusion sets are generally known in the medical arts for use in the administration of a selected medication or other therapeutic fluid to a desired subcutaneous infusion site located beneath the skin of a patient. Such infusion sets typically include a tubular cannula or catheter that is supported by and protrudes from a compact housing adapted to receive the infusion fluid via delivery or infusion tubing, which is suitably connected to other components of the fluid infusion system. Infusion sets can be used, for example, to transport insulin from an insulin pump to a subcutaneous site in a patient.
The subcutaneous infusion set normally includes an insertion needle, which is assembled with the soft cannula and is adapted to pierce the patient""s skin for transcutaneous cannula placement. The insertion needle is thereafter withdrawn to leave the cannula in place for subcutaneous fluid infusion. Exemplary subcutaneous infusion sets of this general type are described in U.S. Pat. Nos. 4,755,173; 5,176,662; and 5,257,980, which are incorporated by reference herein. Such subcutaneous infusion sets are commonly used with compact medication infusion pumps for programmable administration of medication such as insulin. Exemplary infusion pumps of this general type are described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903, which are incorporated by reference herein.
Although the material used for such cannulae are flexible enough to provide comfort for the patient, the inevitable movement of the cannula that occurs as a patient moves results in inflammation. Where a needle is inserted for cannula placement, an injury is created. The implanted cannula, a foreign body, elicits an exacerbated host response, while greater inflammation occurs as a result of any cannula movement. There remains a need, therefore, for improved cannula materials that will reduce irritation to the patient, reduced incidence of infection and reduced incidence of site loss through reduced host response (e.g., deactivation of macrophages and foreign body giant cells at the implant site).
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the invention provides an infusion cannula modified to incorporate one or more medicinal agents. The infusion cannula comprises a tube having an inner lumen and an external surface. The tube comprises an elastomeric material, wherein the elastomeric material is preferably a flexible, biologically compatible material. The tube additionally comprises a coating adhered to the external surface of the tube, wherein the coating comprises a medicinal agent and a polymer matrix. In a preferred embodiment, the medicinal agent is embedded in the polymer matrix, and the polymer is capable of sustained release of the medicinal agent.
Examples of medicinal agents include, but are not limited to, anti-inflammatory, anti-bacterial, anti-viral and disinfecting agents, such as dexamethasone, cefazolin, acyclovir, and benzalkonium chloride. Examples of elastomeric materials include, but are not limited to, polyurethane, polyurea, polyether(amide), PEBA, thermoplastic elastomeric olefin, copolyester, and styrenic thermoplastic elastomer. In some embodiments, the coating further comprises a solvent system, such as tetrahydrofuran and/or isopropyl alcohol. In some embodiments, the tube has a gauge of about 24, and a length of about 0.35 inches.
The invention additionally provides a method for producing an infusion cannula. The method comprises coating a tube with a medicinal agent embedded in a polymer matrix, wherein the tube comprises an elastomeric material and has an external surface and, an internal lumen. In some embodiments, the coating comprises dipping the tube into the polymer matrix, or spraying or painting the polymer matrix onto the tube. The method of coating the tube can be selected so as to optimize the surface to which the coating is adhered. For example, the coating method may be adapted to obtain a cannula having a coating adhered to the internal lumen as well as to the external surface. Coating the tube by dipping, for example, can provide a cannula having a coating adhered to the internal lumen and to the external surface. The invention thus additionally provides an infusion cannula produced by the above method.
In addition, the invention provides a method for infusing a substance into a subject. The method comprises inserting a cannula of the invention into subcutaneous tissue of the subject and delivering the substance into the cannula. The substance is thereby infused into the subject through the cannula. Because the cannula of the invention comprises a tube coated with a medicinal agent in a polymer matrix, the method reduces adverse side effects of subcutaneous cannula insertion.